1. Field of the Invention
The present invention relates to a fermentation process for preparing erythritol with high productivity using Trichosporonoides madida DS 911, more specifically, for preparing erythritol by optimizing the culture conditions such as pH, temperature, aeration rate and agitation speed, and by developing the process of fed-batch culture such as feeding strategy of substrate and composition of feeding substrate.
2. Description of Prior Art
Erythritol, a four carbon sugar alcohol, is a naturally occurring substance and is widely distributed in nature. Like most of the other polyols, it is a metabolite or storage compound for seaweeds and mushrooms. Fruits like melons, grapes and pears also contain erythritol. As it is often produced by bacteria, fungi, and yeasts, erythritol also occurs frequently in fermented food like wine, beer and soy sauce.
Erythritol is a moderately sweet bulking agent with 70.about.80 percent of the sweetness of sucrose in a 10 percent solution. Its high negative heat of solution provides the crystalline material with a strong cooling effect. As it has a taste which is very close to sucrose and with no bitter aftertaste, it is ideal to improve the taste in combination with intensive sweetener like aspartame.
Erythritol production from natural sources such as fruits and vegetables is not practical due to their relative small amounts. Erythritol can be chemically produced by reduction of meso-tartarate, oxidation and reduction of 4,6-o-ethylidene-D-glucose, hydrolysis of dealdehyde starch, or hydrogenation process. Since erythritol production by the chemical methods has been found to be expensive, it is worthwhile to explore an alternative method for the effective production of erythritol using microorganisms.
Erythritol can be biologically produced by microorganisms, especially genus of Candida (U.S. Pat. No. 3,756,917); genus of Aureobasidium (JP Pat. No. 2,626,692 and U.S. Pat. No. 4,923,812); genus of Trichosporonoides (Y. K. Park, Biotechnology Letters 15 (1993) pp 383-388) and genus of Moniliela (Hajiny, Applied Microbiology 12 (1964) pp 240-246).
However, the methods using such microorganisms have a few drawbacks in large scale production. More specifically, the method disclosed in U.S. Pat. No. 3,756,917 using the genus of Candida has low productivity due to its long cultivation period, even though the conversion ratio from n-paraffin is so high.
In the case of the genus of Aureobasidium, the method shows high fermentation yield of erythritol in the concentrated glucose medium compared to other microorganisms. However, the low production rate causes low productivity of erythritol in the case of batch mode fermentation (JP Pat. No. 2,626,692). Even though the productivity is highly increased in the case of cell-recycled continuous culture, there is no successful application in the large scale more than 50 m.sup.3 in industry (U.S. Pat. No. 4,923,812).
On the other hand, the method using the genus of Trichosporonoides shows low productivity due to its long cultivation period even though the conversion ratio is comparatively high. Even though the method using the genus of Moniliela shows high conversion ratio in the high cencentrated glucose medium, the foam vigorously occures during the fermentation, which has to be removed using lots of xanthan gum.